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Appendix II.

P. 699. The Gas Engine.—Beau de Rochas shewed the
necessity for large cylinder volume and small circumference, high
piston speed, large expansion, and high initial pressure, proposing

also his four-stroke cycle, where he used compression to give
opportunity for sustained expansion. The defects of this cycle
are irregular crank effort, dilution of charge with burnt gases, and
expansion-ratio no larger than compression-ratio.

Other Cycles.—In Clerk's engine of 1880, Fig. 874, the charge



is first prepared in the displacer cylinder whose strokes are :
s»—>•       admission of charge, first gas and air, afterwards air,
4-m      slight compression, and expulsion to motor.
The motor crank follows that of displacer by 90°, and the

motor-cylinder operations are